1. Field of the Invention
The present invention generally provides improved medical devices, systems, and methods, typically for treatment of heart valve disease and/or for altering characteristics of one or more valves of the body. Embodiments of the invention include implants for treatment of mitral valve regurgitation.
The human heart receives blood from the organs and tissues via the veins, pumps that blood through the lungs where the blood becomes enriched with oxygen, and propels the oxygenated blood out of the heart to the arteries so that the organ systems of the body can extract the oxygen for proper function. Deoxygenated blood flows back to the heart where it is once again pumped to the lungs.
The heart includes four chambers: the right atrium (RA), the right ventricle (RV), the left atrium (LA) and the left ventricle (LV). The pumping action of the left and right sides of the heart occurs generally in synchrony during the overall cardiac cycle.
The heart has four valves generally configured to selectively transmit blood flow in the correct direction during the cardiac cycle. The valves that separate the atria from the ventricles are referred to as the atrioventricular (or AV) valves. The AV valve between the left atrium and the left ventricle is the mitral valve. The AV valve between the right atrium and the right ventricle is the tricuspid valve. The pulmonary valve directs blood flow to the pulmonary artery and thence to the lungs; blood returns to the left atrium via the pulmonary veins. The aortic valve directs flow through the aorta and thence to the periphery. There are normally no direct connections between the ventricles or between the atria.
The mechanical heartbeat is triggered by an electrical impulse which spreads throughout the cardiac tissue. Opening and closing of heart valves may occur primarily as a result of pressure differences between chambers, those pressures resulting from either passive filling or chamber contraction. For example, the opening and closing of the mitral valve may occur as a result of the pressure differences between the left atrium and the left ventricle.
At the beginning of ventricular filling (diastole) the aortic and pulmonary valves are closed to prevent back flow from the arteries into the ventricles. Shortly thereafter, the AV valves open to allow unimpeded flow from the atria into the corresponding ventricles. Shortly after ventricular systole (i.e., ventricular emptying) begins, the tricuspid and mitral valves normally shut, forming a seal which prevents flow from the ventricles back into the corresponding atria.
Unfortunately, the AV valves may become damaged or may otherwise fail to function properly, resulting in improper closing. The AV valves are complex structures that generally include an annulus, leaflets, chordae and a support structure. Each atrium interfaces with its valve via an atrial vestibule. The mitral valve has two leaflets; the analogous structure of the tricuspid valve has three leaflets, and apposition or engagement of corresponding surfaces of leaflets against each other helps provide closure or sealing of the valve to prevent blood flowing in the wrong direction. Failure of the leaflets to seal during ventricular systole is known as malcoaptation, and may allow blood to flow backward through the valve (regurgitation). Heart valve regurgitation can have serious consequences to a patient, often resulting in cardiac failure, decreased blood flow, lower blood pressure, and/or a diminished flow of oxygen to the tissues of the body. Mitral regurgitation can also cause blood to flow back from the left atrium to the pulmonary veins, causing congestion. Severe valvular regurgitation, if untreated, can result in permanent disability or death.
2. Description of the Related Art
A variety of therapies have been applied for treatment of mitral valve regurgitation, and still other therapies may have been proposed but not yet actually used to treat patients. While several of the known therapies have been found to provide benefits for at least some patients, still further options would be desirable. For example, pharmacologic agents (such as diuretics and vasodilators) can be used with patients having mild mitral valve regurgitation to help reduce the amount of blood flowing back into the left atrium. However, medications can suffer from lack of patient compliance. A significant number of patients may occasionally (or even regularly) fail to take medications, despite the potential seriousness of chronic and/or progressively deteriorating mitral valve regurgitation. Pharmacological therapies of mitral valve regurgitation may also be inconvenient, are often ineffective (especially as the condition worsens), and can be associated with significant side effects (such as low blood pressure).
A variety of surgical options have also been proposed and/or employed for treatment of mitral valve regurgitation. For example, open-heart surgery can replace or repair a dysfunctional mitral valve. In annuloplasty ring repair, the posterior mitral annulus can be reduced in size along its circumference, optionally using sutures passed through a mechanical surgical annuloplasty sewing ring to provide coaptation. Open surgery might also seek to reshape the leaflets and/or otherwise modify the support structure. Regardless, open mitral valve surgery is generally a very invasive treatment carried out with the patient under general anesthesia while on a heart-lung machine and with the chest cut open. Complications can be common, and in light of the morbidity (and potentially mortality) of open-heart surgery, the timing becomes a challenge—sicker patients may be in greater need of the surgery, but less able to withstand the surgery. Successful open mitral valve surgical outcomes can also be quite dependent on surgical skill and experience.
Given the morbidity and mortality of open-heart surgery, innovators have sought less invasive surgical therapies. Procedures that are done with robots or through endoscopes are often still quite invasive, and can also be time consuming, expensive, and in at least some cases, quite dependent on the surgeon's skill. Imposing even less trauma on these sometimes frail patients would be desirable, as would be providing therapies that could be successfully implemented by a significant number of physicians using widely distributed skills. Toward that end, a number of purportedly less invasive technologies and approaches have been proposed. These include devices which seek to re-shape the mitral annulus from within the coronary sinus; devices that attempt to reshape the annulus by cinching either above to below the native annulus; devices to fuse the leaflets (imitating the Alfieri stitch); devices to re-shape the left ventricle, and the like.
Perhaps most widely known, a variety of mitral valve replacement implants have been developed, with these implants generally replacing (or displacing) the native leaflets and relying on surgically implanted structures to control the blood flow paths between the chambers of the heart. While these various approaches and tools have met with differing levels of acceptance, none has yet gained widespread recognition as an ideal therapy for most or all patients suffering from mitral valve regurgitation.
Because of the challenges and disadvantages of known minimally invasive mitral valve regurgitation therapies and implants, still further alternative treatments have been proposed. Some of the alternative proposals have called for an implanted structure to remain within the valve annulus throughout the heart beat cycle. One group of these proposals includes a cylindrical balloon or the like to remain implanted on a tether or rigid rod extending between the atrium and the ventricle through the valve opening. Another group relies on an arcuate ring structure or the like, often in combination with a buttress or structural cross-member extending across the valve so as to anchor the implant. Unfortunately, sealing between the native leaflets and the full perimeter of a balloon or other coaxial body may prove challenging, while the significant contraction around the native valve annulus during each heart beat may result in significant fatigue failure issues during long-term implantation if a buttress or anchor interconnecting cross member is allowed to flex. Moreover, the significant movement of the tissues of the valve may make accurate positioning of the implant challenging regardless of whether the implant is rigid or flexible.
In light of the above, it would be desirable to provide improved medical devices, systems, and methods. It would be particularly desirable to provide new techniques for treatment of mitral valve regurgitation and other heart valve diseases, and/or for altering characteristics of one or more of the other valves of the body. The need remains for a device which can directly enhance leaflet coaptation (rather than indirectly via annular or ventricular re-shaping) and which does not disrupt leaflet anatomy via fusion or otherwise, but which can be deployed simply and reliably, and without excessive cost or surgical time. It would be particularly beneficial if these new techniques could be implemented using a less-invasive approach, without stopping the heart or relying on a heart-lung machine for deployment, and without relying on exceptional skills of the surgeon to provide improved valve and/or heart function.